void endRow()
{
var rowColumns = 0;
for( var i = _cells.Count - 1; i >= 0; i-- )
{
var cell = _cells[i];
if( cell.endRow )
break;
rowColumns += cell.colspan.Value;
}
_columns = Math.Max( _columns, rowColumns );
_rows++;
_cells.Last().endRow = true;
}